1. Field of the Invention
This invention relates generally to amphibious vehicles in general and more particularly to the adaptation of tracked excavators to pontoons for used in swampy marsh.
2. General Background
Tracked vehicles are regularly used in marsh areas for various operations. However, due to the limited demand for amphibious excavation equipment, it is not economically practical to mass-produce such specialized vehicles. In most cases the marsh version of an excavator of the type discussed herein is an adaptation of a standard, dry earthmover. Therefore, commercial excavators are generally stripped of their track systems and refitted with pontoons having endless guided track systems with special track cleats for use in mud and water, powered by independent track drives used to steer the vehicle. The pontoon configuration varies from manufacturer to manufacturer and displacement is governed by type and size of the excavator.
It has been the custom to provide an endless track composed of three rows of chains attached to numerous traverse channels or spaced apart cleat sections, running in longitudinal channels around the pontoons, wrapped around head and tail sprockets and further providing a means for tensioning and driving the endless track as demonstrated by U.S. Pat. No. 4,817,554. Such an arrangement has a high drag coefficient, unnecessarily increases initial chain cost and increase maintenance cost due to wear of a third chain.
Chains subjected to water tend to rust and wear prematurely leading to premature failure. Therefore, the prior art fails to address the need to reduce cost by increasing longevity of the track system. Further, mud and water is a constant problem for bearings and drive systems for obvious reasons further leading to bearing and drive failure resulting in high maintenance cost. The need for constant lubrication of the drives to prevent the incursion of mud and water into the drives is often ignored by the operators thereby leading to mechanical failure.
There is also a need to protect the drive bearing and gear reducers from damage as a result of hidden objects in the mud and water. The prior art often ignores the need for such protection, for a more perfect seal and the need for a stronger bearing arrangement in these special applications and relies primarily on off-the-shelf bearings and seals. However, as in the case of U.S. Pat. No. 4,817,554 protection is provided for a portion of the wheel motor gear reducer by enclosing the gear reducer inside a housing to which one of the drive sprockets is attached. However, the hydraulic motor is left exposed and its bearing and seals are mounted outboard of the pontoon. Two additional sprockets and their shaft are welded to the gear reducer housing. This arrangement subjects the drive sprocket assembly to hazards, increases the likelihood of bearing failure and reduces the weld area around the sprockets. Misalignment further increases sprocket and chain wear and failure. Further there is no mention of encasing the gear reducer in oil.
There is also a need for an easier way to maintain such equipment in the field, such as replaceable and or adjustable pontoons and drives sprocket assemblies that can be quickly replaced thus reducing down time.
The instant invention provides a pontoon system for converting a dry land excavator for amphibious operation. The conversion package comprises a pair of elongated pontoon assemblies secured to each other in a spaced apart manner by transverse support beams configured to support and attach to a land excavator. Each pontoon has an endless track guided around it longitudinally, threaded around a head and tail sprocket assembly, the tail sprocket assembly being fully protected and driven by a hydraulically driven motor attached thereto. The endless track, configured with only two chain runs per pontoon, is attached to light weight traverse channel cleats which allow the track to be much more flexible than cleats connected transversely to triple chains while reducing cost. A series of polymer guide or wear blocks are also provided, attached to each cleat, which further reduces drag while allowing greater flexibility when turning.
A unique head and tail sprocket assembly is provided which includes a stub shaft and bushing bearings lubricated by an internal oil reservoir which further house the hydraulic gear reducer in the drive sprocket assembly, thereby reducing noise and heat while preventing water and mud intrusion.